THE FIRE-PLACE.
Perhaps no part of the interior fittings of a house is more associated
with ideas of cheerfulness and domestic comfort than the _fire-place_.
Our abundant supply of coal has probably induced Englishmen to prefer
the cheerful fire and the “comfortable fire-side” to any other mode of
heating the interior of houses. The steps by which we have arrived at
the use of modern grates and stoves, and the question how far these
are likely to give way to the methods of warming houses by hot air,
by hot water, or by steam, will form an interesting matter for our
consideration; and we shall be indebted to Dr. Arnott’s treatise on
_Warming and Ventilating_, for many illustrative details.
Open Fire-places.
The manner in which rude nations kindle a fire in or near their huts,
is one of the most wasteful arrangements in which fuel can be used.
Houseless savages, because they know no better, and soldiers at
bivouac, because they must make a virtue of necessity, kindle a fire in
the open air, and place themselves near it, benefiting by that portion
of the radiant heat which falls on their bodies; but all the rest of
the heat is wastefully dissipated.
The next step of improvement is, to kindle a fire in a place more or
less inclosed. Under this arrangement, not only will that part of the
radiant heat which falls on the persons be available, but a portion of
the remainder also, which, falling on the walls and warming them, is
partially reflected; and moreover, heat combined with the smoke will be
for a time retained in the place, and thus still further contribute to
the warmth of the interior. By such an arrangement, nearly the whole
of the heat evolved in the combustion is applied to use; but it is
contaminated with the smoke from the fuel. The savages of North America
place fires in the middle of the floor of their huts, and sit around
in the smoke, of which the excess escapes by the one opening in the
hut that serves as a chimney, window, and door. A few of the peasantry
in the remote parts of Ireland and Scotland still place their fires
in the middle of their floors, and leave for the escape of the smoke
only a small opening in the roof, often not directly over the fire. In
Italy and Spain, almost the only fires seen in sitting-rooms are large
dishes of live charcoal, or braziers, placed in the middle, with the
inmates sitting around, having to breathe the noxious carbonic acid gas
which ascends from the fire and mixes with the air of the room: there
is no chimney, and the windows and doors are the only ventilators. The
method of warming with open fires in the middle of the room was adopted
in some of the English Colleges, and some of the London Inns of Court,
down to a comparatively modern period.
A step further in advance is to have a fire, not only in an inclosed
space as a means of keeping in the heat, but with an aperture over it
to act as a chimney or vent for the smoke. This is the form, under
various modifications, adopted in most English houses; the fire being
kindled in a kind of recess under a chimney. By degrees we have become
accustomed to the adoption of a _grate_, which keeps the fuel at a
certain height above the ground; but the principle involved is just the
same. In olden times the fire used to be kindled on the hearth under a
huge chimney, or on a very low grate; but the general course of modern
improvement has tended to lessen the size of the chimney, and to raise
the grate higher from the hearth.
The philosophy of a chimney is well explained by Dr. Arnott, in his
_Elements of Physics_. He says: “Chimneys quicken the ascent of hot
air, by keeping a long column of it together. A column of two feet high
rises higher, or is pressed up with twice as much force as a column of
one foot, and so, in proportion, for all other lengths; just as two or
more corks strung together and immersed in water, tend upwards with
proportionally more force than a single cork, or as a long spear of
light wood, allowed to ascend perpendicularly from a great depth in
water acquires a velocity which makes it dart above the surface, while
a short piece under the same circumstances rises very slowly. In a
chimney where one foot in height of the column of hot air is one ounce
lighter than the same bulk of the external cold air, if the chimney
be one hundred feet high, the air or smoke in it is propelled upwards
with the force of one hundred ounces. In all cases, therefore, the
_draught_, as it is called, of a chimney is proportioned to its length.”
Defects of Open Fires.
This being the general arrangement of a fire in a recess on one side of
the room, and an open chimney above it, Dr. Arnott enumerates a long
list of evils and inconveniences consequent on such an arrangement.
1. _Waste of fuel._--It has been found that in a common open English
fire, seven-eighths of the heat produced from the fuel ascend the
chimney, and are absolutely lost. This lost fuel is thus accounted for.
One half of the heat is carried off in the smoke from the burning mass;
one quarter is carried off by the current of the warmed air of the
room, which is constantly entering the chimney between the fire and the
mantel-piece, and mixing with the smoke; lastly, one eighth part of the
combustible matter is supposed to form the black and visible part of
smoke, in an unburned state. Some writers have even gone so far as to
estimate the loss of heat in an open fire at fourteen-fifteenths of the
whole. 2. _Unequal heating at different distances from the fire._--This
forms a remarkable contrast with the uniform temperature in the air of
a summer afternoon. In rooms with a strong fire, in very cold weather,
it is not uncommon for persons to complain of being “scorched” on one
side, and “pierced with cold” on the other; this is particularly the
case in large apartments; for as the intensity of radiating heat (like
light) is only one-fourth as great at a double distance, the walls of
the room farthest from the fire are but little warmed, and, therefore,
reflect but little heat to the backs of persons grouped round the fire.
3. _Cold draughts._--Air being constantly required to feed the fire,
and to supply the chimney-draught, the fresh air which enters by the
crevices and defects in the doors, windows, floors, &c., is often felt
most injuriously as a cold current. “There is nothing more dangerous to
health than to sit near such inlets, as is proved by the rheumatisms,
stiff necks, and catarrhs, not to mention more serious diseases, which
so frequently follow the exposure. There is an old Spanish proverb,
thus translated,
If cold wind reach you through a hole,
Go make your will, and mind your soul,
which is scarcely an exaggeration.” The current of fresh air which
enters to feed the fire becomes very remarkable when doors or windows
are opened, for the chimney can take much more than it otherwise
receives when the doors and windows are shut; and thus the room with
its chimney becomes like an open funnel, rapidly discharging its
warmed air. 4. _Cold to the feet._--The fresh air which enters in
any case to supply the fire, being colder and specifically heavier
than the general mass already in the room, lies at the bottom of
this as a distinct layer or stratum, demonstrable by a thermometer,
and forming a dangerous cold-bath for the feet of the inmates, often
compelling delicate persons to keep their feet raised out of it by
footstools, or to use unusual covering to protect them. 5. _Bad
ventilation._--Notwithstanding the rapid change of air in the room,
perfect ventilation is not effected. The breath of the inmates does not
tend towards the chimney, but directly to the ceiling; and as it must
therefore again descend to come below the level of the mantel-piece
before it can reach the chimney, the same air may be breathed over
and over again. In a crowded room, with an open fire, the air is for
this reason often highly impure. As another source of impure air in
a house, it may be noticed that the demand of the chimneys, if not
fully supplied by pure air from about the doors and windows, operates
through any other apertures. 6. _Smoke and dust._--These are often
unavoidable from an open chimney, much affecting the comfort and
health of the inhabitants of the house, and destroying the furniture.
Householders would make great sacrifices in other respects to be
free from the annoyance of smoke. In large mansions, with many fires
lighted, if the doors and windows fit closely, and sufficiency of air
for so many chimneys cannot therefore enter by them, not only do the
unused chimneys become entrances for air, but often the longest and
most heated of them in use overpower the shorter and less heated, and
cause the shorter chimneys to discharge their smoke into the room. 7.
_Loss of time._--During the time every morning while the fires are
being lighted, the rooms cannot be used; and there are, besides, the
annoyances of smell, smoke, dust, and noise, all of which are again
renewed if the fire is allowed to go out and to be relighted in the
course of the day. 8. _Danger to person and to property._--How numerous
are the losses of property by carelessness as to fires is well known
to all, while the loss frequent but more distressing loss of life too
well attests the danger to children and to females thinly clad often
consequent on an open fire.
Such are the principal defects which Dr. Arnott enumerates as being
inherent in the use of open fires. Many of them have been greatly
lessened by improved arrangements; but others are still without an
appropriate remedy.
The usual construction of a fire-place is tolerably familiar. In most
cases, the vertical or nearly vertical channel for the chimney is
inclosed within a casing of brick-work, which projects into the room at
one side. The opening for this chimney gradually narrows upwards, until
only large enough to admit the poor little climbing-boy whose task
it was, until within a recent period, to sweep down the unburnt fuel
which our own ill arrangements have wasted; but, happily for humanity
and justice, this system is at an end, and machines are now employed
for the purpose. A hearth of stone is laid whereon to erect the stove
or grate, and this grate is, as we all know, composed mainly of an
iron receptacle for the fuel, and of “hobs,” for supporting culinary
vessels. We cause fire to be kindled in the grate, and then suppose
that all will go on well, without troubling ourselves to inquire
whether the arrangements for the supply of cold air, and the exit of
warmed air and smoke, are such as are best fitted for those purposes.
Remedies for some of these Defects.
In course of time, as the evils of this plan became one by one known,
attempts were made to remedy some of them, and with an approach towards
success. In a recent treatise on the subject by Dr. Fyfe, of Edinburgh,
various modes are suggested for remedying many of the evils incident to
open fire-places. These we must briefly notice.
Sometimes the rooms of a new house are subject to the nuisance of smoky
chimneys simply from deficiency of air. The workmanship of the rooms
being all good, the joints of the flooring-boards and of the wainscot
panels are all true and tight, the more so as the walls, perhaps, not
yet thoroughly dry, preserve a dampness in the air of the room, which
keeps the wood-work swelled and close. The doors and the sashes, too,
work closely and correctly, so that there is no passage left open for
the air to enter except the key-hole, and even this is often closed
over by a little brass cover. Thus, air being denied admission into
the room, there is nothing to feed the fire and to cause a “draught,”
and the smoke cannot ascend the chimney. Instances have been known
of well-built houses being rendered almost untenantable from this
cause, and several hundred pounds being spent in endeavouring to
find a remedy. If, on opening the door or window of a smoky room, it
be generally found that the smoke disappears, this may be taken as
an indication that the close-fitting joints of the wood-work do not
admit air enough for the fire when doors and windows are closed. In
such a case, the opening of the door or window is a poor attempt at
a remedy; for the air proceeds direct to the chimney, and in its way
causes cold to the back and feet of those who may be sitting before
the fire. Numerous methods have been devised for admitting additional
air to the rooms without this inconvenience, among which Dr. Arnott
recommends tubes leading directly from the outer air to the fire-place,
and provided with what are called “throttle-valves,” for the regulation
of the quantity. The following plan has also been recommended as one of
the most practicable. As the air in the upper part of a room is warmer
than in the lower, it is desirable that the supply should come in that
direction, so as to be slightly warmed in its progress towards the
fire, and thus produce less chill to those in its immediate vicinity.
This may be done by drawing down the upper sash of the window about an
inch; or, if not moveable, by cutting such a crevice through its frame;
in both which cases, a thin shelf of the length of the opening may be
placed to conceal it, sloping upwards, to direct the air horizontally
along and near the ceiling. In some houses, the air may be admitted in
such a crevice made in the wainscot or cornice near the ceiling, and
over the fire-place; this, if practicable, is the better of the two,
since the cold air in entering will there meet with the warmest rising
air from before the fire, and be soonest tempered by the mixture.
Another contrivance is to take out an upper pane of glass in one of
the sashes, set it in a tin frame, giving it two springing angular
sides, then replacing it, with hinges below, on which it may turn; by
drawing in this pane more or less, the quantity of air admitted may be
regulated, and its position will naturally direct the admitted air up
and along the ceiling. The circular vane or ventilator sometimes fixed
in windows admits cold air in a similar manner, when the supply for the
room and fire would be otherwise deficient.
The opening or breadth and height of the fire-place, though we may
fancy it leads to the diffusion of more heat into the room, is really a
cause of loss of fuel, and of smoke. The size of the fire-place opening
is often considered in relation to the size of the room, without
regard to the principles on which a fire is maintained in a grate; a
course about as rational (it has been well observed) as to proportion
the step in a staircase to the height of the story, instead of to the
convenience of our legs in mounting them. As the chimneys of different
rooms are unavoidably of different heights, and as the force of the
draught is in proportion to the height of chimney filled with warmed
and rarefied air, it is found that the opening for a tall chimney
may be larger than for a lower one. If the opening be unnecessarily
large, there is room not only for the entrance of fresh air, but also
for the exit of smoke driven down by an opposing current from the
chimney itself; and the air, too, ascends into the chimney in too cold
a state, because the largeness of the opening enables it to enter
without passing very close to the fire. The principal evil attending
the use of a fire-place having too small an opening, is that the fuel
is burned away with unnecessary rapidity. When the opening is found by
experience to be so large as to lead to the descent of smoke into the
room, the easiest remedy is to place moveable boards or sheets of tin
or iron, so as to lower and narrow it gradually. The effect of which,
by excluding a part of the colder air from the chimney, is to produce
a quicker action, so that the fire begins to roar as if blown by a
bellows. “This means is often used to blow the fire instead of bellows,
or to cure a smoky chimney, by increasing the draught. What is called a
_register stove_ is a kindred contrivance. It has a flap placed in the
throat of the chimney, which serves to widen or contract the passage
at pleasure. Because the flap is generally opened only enough to allow
that air to pass which rises directly from the fire, the chimney
receives only very hot air, and therefore acts well. The register stove
often cures smoky chimneys; and by preventing the too ready escape of
the moderately warmed air of the room, of which so much is wasted by a
common fire-place, it also saves fuel.” There does not appear to have
been any attempt to determine by experiment the proper opening of the
fire-place for a given height of chimney; and, indeed, there are so
many disturbing causes, that it would be scarcely possible to determine
this with precision. Dr. Franklin, however, proposed to make the
fire-place openings in the lower rooms about thirty inches square and
eighteen inches deep; those in the upper, eighteen inches square, and
not quite so deep; and those in the intermediate rooms, of dimensions
between these two extremes.
In some cases, where other matters are properly attended to,
inconvenience results from the chimney being too low; as, for instance,
in the case of an attic chimney. In this instance the column of heated
and rarified air is not high enough to give a rapid ascensive power
within the chimney, and thus the smoke cannot be carried up. The best
method of cure is to add to the length of chimney, if this can be done,
and if the fire be in a low building near the ground, this may perhaps
be effected; but in an attic, the means of supporting a lofty chimney
would be inefficient. Another recourse is to contract the opening of
the fire-place to the smallest available dimensions, so that all the
entering air may pass through or close to the fire before entering the
chimney, and thus acquire an ascensive power which will counterbalance
the shortness of the vertical column. It has been recommended that in
some cases there may be three chimneys to one room, so that the united
length of the whole may be equal to that of a tall chimney; but it is
not easy to conceive how this can be practically effected, nor how
the desired result would follow, even if the arrangements were made.
In some cases, the chimney of a room is rendered practically shorter
by being bent round and made to enter the chimney of another room;
since, unless there be a fire in this room also, the warm air from
the shorter chimney has often an adverse current to contend against at
the junction with the other chimney. This is one reason why every open
fire-place should have its own chimney independently of others.
If there be a lofty building or hill near a house, and over-topping
the chimney of one of the rooms, that room is very likely to become
smoky, on account of a current being driven in at the top of the
chimney, and forcing the smoke down with it. Two rival chimneys may
produce a similar effect in a remarkable way. Suppose that there were
two fires in one room, one burning with more force, and therefore
having a more ascensive column of air above it, than the other; if
the doors and windows be shut, the stronger fire will overpower the
weaker, and for its own demand will draw down air from the chimney of
the latter, which air in descending brings down smoke into the room.
The same would be observable in a greater degree if one fire-place had
a fire in it but the other had none, both being at the same time open.
If, instead of being in one room, the chimneys are in two different
rooms communicating by a door, the case is the same whenever that
door is open. In a house where all the openings, such as doors and
windows fitted tightly, a kitchen chimney has been known to overpower
every other chimney in the house, and to draw air and smoke into an
upper room as often as the door communicating with the room was open.
The remedy for this inconvenience lies in the arrangement of the
fire-places, so that each fire shall have exactly enough air for the
consumption of the fuel, without having to borrow from other rooms.
The arrangement of the door of a room influences materially the proper
action of a fire in the fire-place. When the door and chimney are on
the same side of the room, and if the door be in the corner, and is
made to open against the wall, (an arrangement which is often made
for the sake of convenience,) it follows, that when the door is only
partly opened, a current of air rushes along the wall into and across
the opening of the fire-place, and drives some of the smoke out into
the room. This acts more certainly when the door is being closed, for
then the force of the current is augmented, and becomes an annoyance
to persons who may happen to be situated in its path. When the door
and fire-place of a room have been thus ill-arranged with respect to
each other, the evil may be lessened by placing an intervening screen
between the door and the fire, or by reversing the position of the
hinges on the door, so as to make it open in the opposite direction.
Sometimes the smoke from a chimney is driven out into the room, even
when the chimney is not commanded by a superior elevation, it being
driven down by strong winds passing over the top of the chimney. Dr.
Franklin mentioned one or two instances of this kind which he had met
with:--“I once lodged at a house in London, which in a little room
had a single chimney and funnel. The opening was very small, yet it
did not keep in the smoke, and all attempts to have a fire in this
room were fruitless. I could not imagine the reason, till at length
observing that the chamber over it, which had no fire-place in it,
was always filled with smoke when a fire was kindled below, and that
the smoke came through the cracks and crevices of the wainscot, I had
the wainscot taken down, and discovered that the funnel which went up
behind it had a crack many feet in length, and wide enough to admit
my arm; a breach very dangerous with regard to fire, and occasioned
probably by an apparent irregular settling of one side of the house.”
This does not at first thought seem to be an illustration of the effect
of wind passing over the top of a chimney; but the explanation is to be
sought for in a similar way; the air, by entering this fractured part
freely, destroyed the drawing-force of the chimney.
The manner in which the passing of a current of wind over the top of a
chimney may produce a “smoky room” is this:--the warm air which rises
from the fire, in order to obtain a free issue from the chimney, must
repel the air that is hovering over the chimney-pot. In a time of calm
or of little wind, this is done easily; but when a violent current is
passing over the top of the chimney, its particles have such a strong
horizontal velocity, that the heated air in ascending has not power to
displace it, and thus the smoke, not finding a ready exit by that path,
is driven back into the room.
The following anecdote, told by Dr. Franklin, will show what accidental
causes will sometimes occasion a fire to fail in its desired office of
yielding heat without smoke:--“Another puzzling case I met with at a
friend’s house near London. His best room had a chimney, in which he
told me he never could have a fire, for all the smoke came out into the
room. I flattered myself I could easily find the cause, and prescribe
the cure. I opened the door, and perceived it was not want of air. I
made a temporary contraction of the opening of the chimney, and found
that it was not its being too large that made the smoke to issue.
I went out and looked up at the top of the chimney: its funnel was
joined in the same stack with others, some of them shorter, that drew
very well, and I saw nothing to prevent its doing the same. In fine,
after every other examination I could think of, I was obliged to own
the insufficiency of my skill. But my friend, who made no pretension
to such kind of knowledge, afterwards discovered the cause himself.
He got to the top of the funnel by a ladder, and looking down, found
it filled with twigs and straw, cemented by earth, and lined with
feathers. It seems the house, after being built, had stood empty some
years before he occupied it, and he concluded that some large birds had
taken the advantage of its retired situation to make their nests there.
The rubbish, considerable in quantity, being removed, and the funnel
cleared, the chimney drew well and gave satisfaction.”
From these details it will at once appear, that that part of the
builder’s art which relates to the arrangement and building of the
fire-place is by no means an unimportant one, since the comfort of the
inmates is seriously affected by want of skill on his part. Hence we
may also observe, that chimney doctors are liable to the same kind of
errors as quack doctors in another sphere; for it is almost as absurd
to attempt to cure all smoky chimneys by one course of proceeding,
as to cure all kinds of diseases by one medicine. There may be a
deficiency of air in the room; the opening of the fire-place maybe
too large; the chimney may not have height enough; one chimney may
overpower another in its draught; the chimney may be overtopped by
higher buildings or by a hill; the door of a room may be badly placed
with respect to the window; or, lastly, as in Dr. Franklin’s “puzzling
case,” the chimney may be nearly stopped up. All these are sources of
the much-dreaded “smoky chimney,” and all require modes of treatment
adapted to the nature of the evil. Many of these evils have, to a
considerable extent, been remedied by the use of Rumford stoves, and
other forms of stove and grate, in which, although retaining all the
chief characters of an open fire-place, there is yet a great diminution
of the evils to which the latter is liable. There have, however, been
marked extensions recently made in the construction of _close stoves_,
intended to obviate the ill effects attendant on open fire-places.
These must be briefly noticed.
Close Stoves.
In a close stove, no air is admitted but what passes at once through
the fire; and the chimney or funnel is only just large enough to carry
off the sulphurous and other vapours, for there is hardly any smoke
from a close stove, and, therefore, it is not necessary to make a
chimney large enough to admit a climbing-boy.
A small German stove, suitable for a room twenty-four feet by eighteen,
will give an idea of the general character of this kind of close
stove. The stove rests on a base about thirty-six inches by fourteen.
The fire-place has a bottom to receive the fuel, but no bars, and is
shut by a door which fits closely to its case. This door has a small
wicket at the bottom, the aperture of which is regulated by a sliding
plate, so as to admit no more air than will suffice for the slow
combustion of the fuel. The flame and heated air ascend to the top of
the fire-place, and pass into two hollow pillars or piers, which rise
to a height of five or six feet, so that the heat is communicated to a
large surface, before the volatilized products of combustion make their
exit by a pipe into the chimney. The stove is supplied with fuel and
with air by the front door. If it is desired to make the fire visible,
and impart some of that cheerfulness which belongs to an open grate,
the door of the stove maybe thrown open, for there is no danger of the
smoke coming out after the current has once warmed the upper part of
the stove. When the stove is of such dimensions that the body of it is
about two feet and a half high, the fire-place may be furnished with
a small grate in the English style. If the door is so hung that it
can not only be thrown back, but also lifted off its hinges, it will
approach still more to the character of a stove-grate.
A cheap form of “German stove” is often made in this country, and used
in workshops and small manufactories, where the body of the stove is
an upright cylinder, of which the lower part is the ash-pit, closed or
opened by a hinged-door, the middle part the fire-place, where the fuel
rests on bars, and the upper part a vacant space, which becomes filled
with flame, smoke, and heated air, so as to impart great heat to a flat
iron plate at the top. There is a door at which the fuel is introduced,
and a small flue or funnel of iron pipe, which conveys the smoke into
a chimney or into the open air. Many forms of stove have been used
more or less resembling this in principle; but there is one great
defect pertaining to them all. The metal of which the stove is formed
becomes so highly heated near the stove, that it acquires a _burnt_
smell, owing to the decomposition of animal and vegetable particles
which are at all times floating about in the air. The air, too, in the
room, becomes close and oppressive from another cause; for as only a
small quantity of air is consumed by the stove, the air does not become
renewed in the room so frequently as when an open fire is used, and
thus it is respired over and over again.
To remedy the evils resulting from burnt air, close stoves are made
with a double case, so that there shall be a body of air between the
fire and the air of the room. It is on this principle, modified in
various ways, that a large number of stoves have been constructed;
of which one, by Mr. Sylvester, may be briefly described. There is a
hollow cast-iron box, on the outside of which are cast several ribs.
Those ribs are about three-quarters of an inch thick, and project three
or four inches beyond the surface of the box; and their object is to
increase the heating surface; for the fire being lighted in the hollow
of the box, the conducting power of the iron causes the whole exterior
case of the box, together with the projecting ribs, to become heated.
The box is placed within an ornamental case, the sides and top of which
are fretted with lattice-work, to allow free access to the air, which
enters through the lattices at the sides and escapes from the top of
the stove, passing in its passage over the ribbed surface of the heated
box. The grating on which the fuel lies is formed of a number of loose
bars fitted together into a frame, and prolonged so as to emit heat
into the room as well as to support the fuel. Everything is so arranged
as to give as much iron surface as possible, so as to communicate heat
to the surrounding air; while at the same time the extent of the heated
surface prevents any one part from being excessively and injuriously
heated.
Dr. Arnott’s Stove.
To describe all the “chunk” stoves, “Vesta” stoves, “Olmsted” stoves,
and other similar contrivances of modern times, would fill a volume
instead of a few pages. We may, however, speak briefly of Dr. Arnott’s
stoves as a means of showing some of the inconveniences to which close
stoves are liable, if not constructed with care. This stove consists of
an external case of iron, of any ornamental shape. Within this case is
placed a box made of fire-clay, to contain the fuel, having a grating
at the bottom; and there is a space left between the fire-box and the
exterior case, to prevent the communication of too much heat to the
latter. Thee pedestal of the stove forms the ash-pit; and there is no
communication between the stove and the ash-pit, except through the
grating at the bottom of the fire-box. A small external hole in the
ash-pit, covered by a valve, admits the air to the fire; and according
as this valve is more or less open, the vividness of the combustion is
increased or diminished, and thence the greater or less heat produced
by the stove. The quantity of air admitted by this valve is governed by
a self-regulating apparatus, either by the expansion and contraction
of air confined by mercury in a tube, or by the unequal expansion of
different metals. The smoke escapes through a pipe at the back of the
stove; but the fuel employed is such as to yield very little smoke.
By adjusting the regulator so as to admit only a small quantity or
air, the temperature of the stove is kept within the required limits;
and owing to the slow-conducting power of the fire-clay, of which the
fire-box is formed, the heat of the fuel is concentrated within the
fire-box, and the fuel burns with less air and less rapidity than it
would otherwise do.
The construction of Dr. Arnott’s “thermometer stove” will be better
understood from the following figure, which represents the stove with
one of its sides removed, so as to exhibit its interior arrangements:--
[Illustration]
The outlines of the figure, _a a a a_, represent the case or body of
the stove, which might be formed either of cast or sheet iron. It is
divided into two chambers by the partition, _b b_; but in such a way
that there may be a free communication at the top and bottom. _c_ is a
small furnace, or, as it is called by the inventor, a fire-box, made
of iron, and lined with fire-bricks. The fire-box is not in contact
with the exterior case of the stove. It communicates at the bottom with
an ash-pit, the door of which is at _d_,--that of the stove, by which
the fuel is introduced, is at _d´_. Both these doors must fit very
accurately. Above the door of the ash-pit is a bent pipe _e_, by which
air gains admittance to the fire.
A fire being kindled and the doors at _d d´_ shut, the only way in
which air has access to the fuel is by the pipe _e_; the air so
admitted, passing through the fire before it enters the upper part of
the stove. That portion of the air not required to aid the combustion
of the fuel having reached the main body of the stove, and there
mixing with the smoke and other products, they circulate slowly in the
directions indicated by the arrows, and at length pass into the chimney
by the pipe _f_.
The slow movement just mentioned as taking place within the stove may
well be contrasted with what happens in an open fire-place. In one
case the greater part of the heat produced is rapidly carried off by a
current of air ascending the chimney--by the thermometer stove it is
detained until almost the whole of it has been diffused throughout the
apartment.
The bent tube _g_ terminating in a cup-shaped opening at _g´_, is a
self-regulating valve. The tube is closed at the end _g_ within the
stove, _g´ g´´_ represents mercury which occupies the bend of the tube.
When the fire in the stove burns too briskly, the air in the tube
occupying the space between _g_ and _g´´_ is expanded, and by expelling
some of the mercury from the tube at _g´´_ into the cup at _g´_, it
closes the aperture of the pipe _e_; thus cutting off the supply of air
to the fire. In a few minutes (the fire in the mean time having abated
its energy,) the air in the tube will return to its former dimensions,
and the mercury subsiding in the cup, air is again permitted to enter
the ash-pit.
The stove, of which we have thus attempted to convey a general
idea, may be made of any required form or size. Instead of the
self-regulating air-valve just described, it is fitted up with others
of a very simple construction, and which admit of being adjusted with
the greatest accuracy by the hand.
The objections to this form of stove arise chiefly from the formation
of deleterious gases, which are not carried off completely. The slow
combustion of the fuel produces a large quantity of carbonic oxide,
which is liable to escape into the room, and is of an injurious
character. Carburetted hydrogen gas is also formed in these stoves.
Many modifications of form have been suggested for the remedy of these
evils; but the slow combustion, which was one of the merits originally
claimed for the stove, and which it certainly deserves, seems an
unavoidable cause for the production of these gases.
All the varieties of open fire-place, as adopted in English houses, the
hearth, the recess, and the chimney, are at one side or at one corner
of the room; but in the adoption of close stoves this arrangement
is not necessary; for the stove may be in any part of the middle of
a room, provided the pipe constituting the flue be long enough. In
some cases this pipe is carried upwards to the ceiling, and thence
conveyed to some outlet into the open air; in other cases it is turned
downwards and conveyed under the flooring to a proper place of exit;
while in others the pipe is stretched or extended horizontally from the
stove to the regular chimney of the room.
Warming Buildings by Heated Air.
Our builders have not yet entered so far into the mechanical
contrivances of the age as to dispense with chimneys altogether; nor
could such a thing be done until a total change is effected in the
opinion of persons concerning the cheerfulness of an “open fire.” But
there are nevertheless three modes, more or less adopted in the present
day, whereby a house is warmed without the necessity for anything
like a fire-place. These methods--in all of which the heating agent
is brought from another room into the one to be warmed--are of three
kinds; heating by _hot air_, by _hot water_, and by _steam_.
When we speak of warming an apartment by heated air, it is necessary
to give precision to the meaning of the term. All rooms are, in fact,
warmed by heated air, for the stove or grate must raise the temperature
of the air in the room before we can appreciate the sensation of
warmth. But what is generally meant by the term as here used is the
warming of one apartment by air heated in another. The stoves used in
Russia, though not coming exactly under this description, will serve in
some degree to illustrate the principle.
The Russian stove is intended as a sort of magazine, in which a great
quantity of heat maybe quickly accumulated, to be afterwards slowly
communicated to the apartment. The stove is therefore made of a massive
size. It is formed of brick-work, clay, glazed tiles, which together
form a great mass of matter to be heated by the fuel; and there is in
every part a considerable thickness of slow-conducting material between
the fuel and the air of the room. The fire is kindled early in the
morning, after which the stove door is shut, and the air aperture below
left open for some time as a means of admitting draught to the fire;
but in the course of a short time the fire-door is opened to check the
draught, so as to prevent the too rapid combustion of the fuel. In
this way the combustion is allowed to go on, and the substance of the
stove becomes warmed, after which the air passages are shut, so as to
prevent any abstraction of heat by the current that would otherwise
be occasioned. The stove thus becomes a great mass of heated matter,
which is gradually pouring warmth into the apartment during the whole
of the day; and as the temperature of the surface never becomes very
high, the impurities in the atmosphere are not decomposed, and it is
consequently free from those offensive effluvia, unavoidable when metal
stoves are used. The fuel is allowed to be nearly burnt out before
the apertures of the stove are closed; and therein the stove differs
greatly from those hitherto considered; the heated air within the stove
being so completely shut in that it can find no outlet, except through
the substance of the brickwork.
The modifications of the arrangements whereby warmed air is conveyed
from one room to another, may next be noticed. In such cases the air
either escapes from a heated receptacle outside the fire-case, or
else it merely passes over a heated metallic surface. The following
description relates to one variety of the first of these two methods.
In the lower part of a house or building is a cast-metal double stove;
the inner part forming the stove, and the outer one the case or
envelope. The fuel is burned in the inner stove, and the smoke produced
during the process of combustion is carried off by a chimney, which
passes through both stoves or cases, and is conveyed to the outside
of the building. The outer case includes not only the furnace or
inner stove, but also a considerable space occupied by the air of the
atmosphere, which is freely admitted through a number of holes placed
around it; and when any current of warmed air is produced, it passes
off from the space between the outer case and the inner stove, and is
conveyed by tubes to any apartment in the building; so that the rooms
are warmed by the air which has passed between the outer case and the
inner stove.
In another form of arrangement, having the same end in view by means
of heated air, the air, instead of passing through an enclosed space
between the outer case and the inner stove, passes over a surface of
metal which is heated either by a fire underneath, or, which is better,
by steam or hot water contained in pipes. The temporary House of
Commons, the Reform Club-house, and many other buildings, are warmed in
this way.
The following simple and cheap form of stove has been erected in the
cottages of Sir Stewart Monteath’s labourers. The accompanying figure
represents a section of the stove, the principle of which will be
understood from the following explanatory notes:--
[Illustration
1. _Kitchen fire._
2. _Chimney._
3. _Hot air Chamber._ This is a cast-iron box, which forms the back of
the kitchen grate.
4. _Cold air pipe, or passage_; made with brick, or stone, or iron
piping, communicating with the open air for the purpose of feeding the
hot air chamber with an ascending current of fresh air.
5. _Hot air pipe_, receives the ascending current of air, which
becomes heated by passing over the back of the fire. At the top this
pipe branches off at right angles, and terminates near the floor in
the two sleeping rooms above.
6. _Gratings_ to admit the warm air from the hot-air pipe into
the bed-rooms. The addition of sliding valves over the face of the
gratings would serve to cut off the current of warm air during the
summer, and when not otherwise required.
7. _Sitting-room_, into which sufficient heat is radiated from the hot
air chamber, not only to warm the apartment, but even to dry wet
linen.]
By means of one common fire in a stove of the above description, a
four-roomed cottage can be comfortably warmed, and kept dry throughout.
Warming Buildings by Steam.
The arrangements for warming rooms and buildings by steam are very
different from those in which stoves are employed. They are generally
such as the following. At a convenient part of the building, and as
low as possible, there is placed a close steam-boiler of the ordinary
construction. From this boiler a small steam-pipe is carried to the
parts of the building which are to be warmed; the pipe being wrapped
round with a thick layer of flannel, to prevent the heat from radiating
before it arrives at the destined place. Pipes of a larger size are
laid round the rooms above the floor, or under a perforated floor, or
in any other convenient position. The steam issues into these larger
pipes, from the surface of which heat radiates into the room, and thus
the steam is condensed into water. Small pipes of lead or tin are
provided for convoying the water back into the boiler, a gentle slope
being given to all the pipes to facilitate this object. This water,
again flowing into the boiler, is again converted into steam, again
ascends to the pipes which surround the apartment, again gives out heat
to the air of those apartments, and again flows back to the boiler in
the form of water. Thus the same supply of water circulates over and
over again through the pipes, carrying heat from the fire below to the
rooms above. In some cases the steam-pipes in the apartments, instead
of being laid round the sides, are grouped together in a compact form,
and have an ornamental character imparted to them.
Instead of pipes, the steam is sometimes made to circulate between
parallel sheets of copper or iron, in such manner that every sheet of
metal shall have steam on one side of it, and air on the other, the air
in that position receiving heat from the steam through the metal.
Warming Buildings by Hot Water.
Lastly we have to notice the method of warming by _hot water_. In
this method there is usually a boiler communicating by an upper and
lower pipe, with an upright pipe the same height as the boiler. On the
application of heat to the boiler, the column of water becomes lighter
than that in the upright pipe; therefore the pressure on the water in
the lower pipe being less at the end nearest to the boiler than it
is at the other end, a portion of the water in this lower pipe moves
forward towards the boiler, which causes a corresponding quantity to
pass along the upper pipe in a contrary direction. This motion will
necessarily continue as long as the column of water in the boiler
is hotter, and therefore lighter than that in the upright pipe; and
this must be the case so long as the boiler continues to receive heat
from the fire, and the pipes to part with their heat to the air, and
thereby cool the water contained in them. In whatever form the hot
water apparatus is constructed, this difference of pressure of the two
columns of water is the cause of the circulation.
In this form of apparatus some part or other of the water is open to
the atmosphere, either at the top of the boiler or at the top of one
of the pipes, so that there is no danger from the bursting action of
water heated above the boiling temperature. But, on the other hand, the
water cannot well be conveyed to rooms at different elevations in the
building. To increase the efficacy of the arrangement in this respect,
the following adaptation has been suggested. A pipe is made to dip into
an open boiler, reaching only an inch or two below the surface of the
water, and passing round the room to be warmed, returns again to the
boiler and dips again into the water, descending quite to the bottom of
the boiler. An air-pump is connected with this pipe by a small tube;
and the air in the pipe being exhausted by this means, the water rises
into the pipes above the level of the boiler by atmospheric pressure,
and the circulation then takes place by the hot water ascending through
the pipe at the top of the boiler, and passing through the whole
circuit of the pipe, it returns through the upper end of the pipe which
reaches to the bottom of the boiler.
In the last-described form of apparatus the water will rise in the
syphon pipe to a height of about thirty feet above the boiler, being
that elevation which is due to the action of the atmosphere on liquid
flowing through a vacuum. But when a whole house or building is warmed
by hot water in all the different floors or heights, a modification of
the system, called the _high-pressure system_, is adopted.
The apparatus on this system consists of a spiral coil of small iron
pipe built into a furnace, the pipe being carried from the upper part
of the coil, and entwined round the room intended to be warmed, forming
a continuous pipe when again joined to the bottom of the coil. The size
of the pipe is usually only half an inch in diameter internally, and an
inch externally. A large pipe of about two and a half inches diameter
is connected, either horizontally or vertically, with the small pipe,
and is placed at the highest point of the apparatus. This, which is
called the “expansion pipe,” has an opening near its lower extremity,
by which the apparatus is filled with water, the aperture being
afterwards secured by a strong screw; but the expansion pipe itself
cannot be filled higher than this opening. After the water has been
introduced, the screw is securely fastened, and the apparatus becomes
completely closed in all parts. The expansion pipe, which is thus left
empty, is calculated to hold about one-tenth or one-twelfth as much
water as the whole of the small pipes; this being necessary in order
to allow for the expansion that takes place in the volume of the water
when heated, and which otherwise would inevitably burst the pipes,
however strong they might be.
In this apparatus the principle of action is different from that in the
low-pressure method. Here the water is raised to so high a temperature
that it wholly overcomes the effect of gravity, and rises to the
highest rooms of a building if required, the circulation through the
system of pipes being more rapid as the heat of the water is greater.
But there are inconveniences attending the method. If the pipes be not
very strong, they will be burst by the intense pressure from within;
as they will likewise if the expansion pipe be too small. If, on the
contrary, this latter pipe be too large, it occasions the water to be
driven up into it so violently as to leave the lower part of the coil
of small pipe almost empty, and therefore liable to be burned by the
heat of the fire. And if all these points be properly attended to,
there is still the inconvenience resulting from the decomposition of
the floating particles in the air, by the highly-heated metal of the
pipes. In some cases water, instead of being heated in a coil of small
pipes, passes into and through large flat boxes or chambers, whose
extended surface enables the surrounding air to be heated more rapidly.
The details of this chapter will enable the reader to perceive, that
that part of the builder’s art which relates to the construction of the
_fire-place_ rests on more scientific principles, and is more liable to
change by successive discoveries and inventions, than most others. It
is not simply to make a square opening by the side of a room, to have a
vertical chimney or flue above that opening, and a few bars within it;
it is not by such means that the object to be answered by a fire-place
can be attained; some knowledge of chemistry, pneumatics, and
hydraulics, is required before we can properly regulate the combustion
of our fuel, the ventilation of our apartments, or effectually warm
them by the ascension of hot air, the circulation of hot water, or the
condensation of steam.